This invention relates to new isocyanurate-group-containing polyisocyanates based on polyisocyanate mixtures containing 2,4-diisocyanatotoluene which are liquid and storable at room temperature, to a process for their production and to their use as a synthesis component in the production of polyurethane plastics by the isocyanate polyaddition process.
Isocyanurate-modified diisocyanatotoluenes and their use for the production of polyurethane plastics are already known in principle [cf. for example DE-OS No. 22 21 811, DE-OS No. 24 52 532 (corresponding to U.S. Pat. No. 3,996,223), DE-OS No. 24 03 858 (corresponding to U.S. Pat. No. 3,970,600), DE-OS No. 20 63 731, DE-AS No. 10 22 789, U.S. Pat. No. 4,243,756 (Example 5) or U.S. Pat. No. 3,652,424].
The isocyanurate-modified polyisocyanate mixtures based on diisocyanatotoluene and, more particularly, on a technical 80:20-mixture of 2,4- and 2,6-diisocyanatotoluene which are specifically described in these prior publications are attended by the disadvantage that either they are not homogeneous liquids which can be stored at room temperature or, to guarantee that property, contain considerable quantities of stabilizing additives. Stabilizing additives of the type in question here are, for example, urethane- and/or allophanate-modified polyisocyanates of the type obtained in situ by modifying the polyisocyanates with polyols before or after the trimerization reaction. Other stabilizing agents are, for example, the compounds containing amide and/or acyl urea groups as described in U.S. Pat. No. 3,970,600. One feature common to these stabilizing additives is that they contain active hydrogen atoms attached to nitrogen which show a relatively pronounced tendency to react with isocyanate groups. Accordingly, although mixtures containing the above-mentioned additives often show adequate stability in storage, they lack stability in regard to their NCO-content because uncontrollable secondary reactions between the isocyanate groups and the active hydrogen atoms in the additives cannot be avoided.
Pure isocyanaurate-modified polyisocyanate mixtures based on diisocyanatotoluene which are homogeneous liquids at room temperature and which show adequate stability in storage have never been known before. In the present context, adequate stability in storage is understood to mean that the polyisocyanates protected against atmospheric moisture remain liquid at temperatures in the range from 20.degree. to 40.degree. C. and remain free from clouding and precipitates over a period of at least 6 months. In addition, product crystallized by cooling to &lt;0.degree. C. must always melt completely clearly again at temperatures in the above-mentioned range.
Accordingly, the object of the present invention is to provide isocyanurate-modified polyisocyanates based on diisocyanatotoluene which are liquid and stable in storage at room temperature and which do not contain any significant quantities of compounds containing active hydrogen atoms so that the uncontrollable secondary reactions (by which stability of the NCO-content is adversely affected) can be avoided.